In one aspect, the invention relates to an olefin conversion process. In another respect, the invention relates to the purification of hydrocarbon streams.
Prior to the invention, high purity feeds were required for disproportionation conversion reactions. For the conversion of butene-2 with ethylene to produce propylene, for example, a butene-2 purity in excess of 75% by weight was required, and oxygenates in the feed could not be tolerated. Sources of such a feedstock were quite limited and expensive.
One such source, for example, was an ethylene dimerization unit operated with a nickel octanoate triphenyl phosphate catalyst. With increasing ethylene costs, an alternative, less expensive, butene-2 source was clearly needed.
One such source that was identified was formed by removing the isobutene from a mixed C.sub.4 stream by reaction with methanol and the butadiene by absorption with acetonitrile. This stream, however, contained a low level of butene-2, on the order of 15% wt %, and high levels on the order of 0.1 wt % or more, of oxygenates, which are known disproportionation catalyst poisons.
In a preferred embodiment, this invention relates to process modifications made to permit propylene production from this feedstock via disproportionation.